Isolation and regulation of Sinorhizobium meliloti 1021 loci induced by oxygen limitation

Eleven Simorhizobium meliloti 1021 loci whose expression was induced under low oxygen concentrations were identified in a collection of 5,000 strains carrying Tn5-1063 (luxAB) transcriptional reporter gene fusions. The 11 Tn5 -1063-tagged loci were cloned and characterized. The dependence of the expr ession of the tagged loci on the FixL/FixJ oxygen-sensing two-component reg ulatory system was examined. Three of the loci were found to be dependent u pon fixL and fixJ for their expression, while one locus showed a partial de pendence. The remaining seven loci showed fixL- and fixJ- independent induc tion of expression in response to oxygen limitation. This suggests that in S. meliloti, additional regulatory system(s) exist that respond either dire ctly or indirectly to oxygen limitation conditions.